Jim Moore

April 1, 2008

In the Save Energy Now (SEN) initiative of the U.S. Department of Energy’s (DOE’s) Industrial Technologies Program (ITP), Energy Savings Assessments (ESAs) of steam as well as other industrial plant systems are performed to identify energy conservation opportunities. Steam System Assessments consider the design and operation of the plant in the context of the BestPractices steam criteria. The adequacy of thermal insulation for piping, tanks, and other elements of the distribution systems are among the characteristics evaluated. The analysis approach involves observing the condition of the distribution system and using the 3E Plus® insulation tool and the Steam System Assessment Tool. Readers who are unfamiliar with these tools are encouraged to visit the BestPractices Steam website at www1.eere.energy.gov/industry/bestpractices/steam.html.

The condition of the thermal insulation observed during the Steam System Assessment varies. In some cases, limited repair of damaged insulation and the addition of insulation previously missing on steam supply lines are the only requirements. This may affect as little as 10 percent of the length of steam mains and laterals. In other cases, however, the length of steam piping affected is more significant due to systems having undergone substantial alterations without replacement of insulation. The insulation of valves, pipe sections with gauges and sensors, and “T” sections and elbows is another frequently observed opportunity.

The conditions associated with condensate return systems vary even more widely. In some circumstances, the energy conservation opportunity is limited to selected repair of condensate mains and laterals. However, in other cases, the condensate piping is found to be completely non-insulated, as it was believed to be unnecessary because of the following:

The lower temperature of the pipe

The fact that the losses are often to conditioned spaces

Despite these perceptions, eliminating the uncontrolled loss of energy to various spaces usually represents an energy conservation opportunity. This article provides reflections—from an owner’s perspective—from six recent steam system efficiency improvement projects.

A Good Place To Start

In a food processing plant using high-pressure steam for sterilizing and cleaning operations, the steam system is the backbone of the operation. The system in this plant is old, and had not been well maintained over a period of several years, as evidenced by leaks and deteriorated or missing insulation in many areas.

The new plant engineering manager had received a mandate to reduce utility costs. His initial response was to insulate distribution piping—steam and condensate that carried steam from the boiler plant to the end-use loads through the maintenance shop. Based on the system assessment, several measures were recommended, including eliminating leaks, improving boiler efficiency, and performing additional insulation repairs.

The plant engineering manager needed a “quick fix” that was visible as a statement to both corporate management and the maintenance staff that things were improving. The assessment validated the cost-effectiveness of the investment in pipe insulation, showing a payback of 1 year or less on additional insulation that would save $45,000 per year. Since completing the assessment, additional insulation repairs have been performed, along with leak repairs and other operational improvements.

Distribution System Effects

Distribution system energy losses can vary from 10 percent to more than 25 percent of a central boiler plant’s output. A major factor influencing these losses is the length of steam and condensate piping that the plant serves, along with the condition of the insulation. Based on the existing conditions found at one facility—with a system consisting of more than 1 mile of steam piping—reducing the losses from uninsulated segments lowers thermal losses from 15 percent of average boiler output to 4 percent. The insulation work involved less than 20 percent of the mains and laterals. The work on the condensate return system involved about 1/2 mile of pipe. Losses represented about 15 percent of average boiler output, while the fully insulated condensate piping is reduced to 4 percent of boiler load.

At a plant with an installed boiler steam output capacity in excess of 175,000 parts by weight per hundred parts by weight (PPH), and an extensive distribution system made up of both underground and overhead piping, the recommendation to improve plant insulation was the first to be implemented. The owner’s representative recently reported that the insulation work was reducing energy, but the extensiveness of the need at this facility required that the work be phased with the distinct subsystems’ insulation to be repaired in a sequential manner. The owner’s representative realized that some level of attention would be needed on a continuing basis—a key observation for sustaining the benefits the plant was beginning to realize.

Steam Generation Capacity And Actual Conditions

As a corollary to the preceding observations, steam systems serving manufacturing operations with a large space footprint will expend a significant part of the plant output keeping the steam lines hot and supplying auxiliary steam for plant operations. For example, a plant that was recently assessed had two central plants—each with less than 20 million British thermal units per hour (mmBtu/hr) of output capacity—was estimated to use almost one-third of the exported steam keeping the distribution system hot. At this plant, the steam condensate is returned at a low temperature—less than 150°F. This results in the need for a significant auxiliary steam load to raise the condensate temperature to boiler entrance conditions. Not correcting this deficiency would pose a threat to boiler life due to thermal shock.

Repairing the insulation on the steam lines, adding insulation to previously uninsulated condensate return piping, and taking steam and condensate piping out of service to abandoned operations were among the most cost-effective opportunities identified at this site.

At the same location, the condensate-receiving tank was not insulated. This was found to add losses of 400,000 Btu/hr, adding 20 percent to the losses from the piping system. With this justification, the owner’s representative contracted to have the tank insulated.

As with the prior case, the owner’s representative indicated that the recommendations relating to the thermal insulation deficiencies were among the first to be implemented. He expected that the work would continue as an ongoing process.

Relative Value

At another manufacturing plant, improving the insulation on a steam and condensate piping system that consists of about 1 mile of mains and laterals was estimated to save more than 6 mmBtu/hr—about the same savings that would result from the addition of a feedwater economizer in the central plant. However, the payback of a year or less for the insulation measure is much more favorable than the 4- to 6-year payback associated with the economizer.

As a result, the insulation work was initiated, and the economizer is still considered an interesting idea.

More Than Economic Merit

A recent assessment of a beverage bottling facility provides another example of the importance of insulation repair projects to system efficiency programs. The review of the overall system identified numerous opportunities, including burner change-outs, boiler operating changes, process control improvements, and insulation. The deficiencies were identified early in the assessment during field surveys of existing conditions. The insulation opportunity was discussed with the owner’s representative, who responded by hiring insulation contractors to replace the missing insulation.

The work was done quickly, the results were visible, and the payback was fast—less than1 year. As with the food processing plant, the plant started realizing energy cost reductions immediately, and the newly reinsulated pipe caused a boost in maintenance staff morale.

Underground Piping

Many steam systems, especially district systems, transport steam through buried pipes and underground vaults with branch connections and blocking valves. Buried piping can benefit from the insulation qualities of typical soils, unless there are leaks or high groundwater levels. The challenge with underground systems is typically maintaining insulation quality in manholes and underground vaults. These areas are where maintenance activities are most likely to occur and are subject to the usual wear-and-tear and attention-to-detail issues that all too often allow long-term degradation of pipe and valve insulation to occur. While the piping in manholes may only represent 2 to 5 percent of the overall system length, as the examples above have shown, small sections of uninsulated piping and valves have a significant impact on distribution system energy losses.

This was illustrated during another recent activity involving a large steam distribution system with more than 10 miles of steam and condensate mains and laterals. At this site, analysis has shown that improving manhole conditions, including steam and condensate pipe insulation repairs, is estimated to save about $500,000 a year, with a payback of about 1 year.

Final Tips

What does it take to minimize steam system losses due to substandard insulation over an extended period? The following comments from owners’ representatives provide good guidance:

Get started somewhere—but get the work started.

Stay at it. As several of the examples cited above indicate, it is a long-term process.

Savings will be apparent quickly, and returns on the investment are rapid. Additional benefits include cleaner plant spaces and improved morale for facilities engineering and maintenance employees.

To reduce administrative time hiring insulation contractors for what can be many short-term tasks, some representatives also indicated that they established long-term contracts that set out agreement conditions and costs, authorizing specific tasks under “task orders.” Task-order contracts can expedite the front-end time to get a specific insulation task completed.